Large earthquake causes mud island to rise from the sea

Temporary island is seething with methane.

A magnitude 7.7 earthquake hit south-central Pakistan on Tuesday this week. Reports of hundreds of casualties highlight the awful scale of the tragedy, made more difficult for rescuers by the remote location of the quake, 270km north of Karachi.

One of the surprises waiting for people who arrived in the quake’s aftermath was a new island. Just offshore near the site of the earthquake, the island appears to be a large pile of mud, built by the distinctive conditions in the area of the fault.

The quake was caused by movement of the Earth on a fault in the crust at rather shallow depth, around 15km below the surface. The movement at the fracture was a rupturing, as the oceanic crust of the Arabian tectonic plate is dragged down, or “subducted,” beneath the Eurasian continental plate at Pakistan. It is part of what geologists term the “Makran subduction zone,” which extends parallel to the Indian Ocean coast south of Pakistan and Iran.

Earlier this year, the Makran subduction zone was found to be a potential lurking tsunami threat. It has history. A tsunami occurred there on November 28, 1945. Caused by a magnitude 8.1 earthquake, it triggered a landslide under the ocean that generated a 15m-high tsunami, resulting in the deaths of more than 4,000 people along the Makran coast. It was the second worst tsunami event in the Indian Ocean, after the more recent December 2004 Sumatra earthquake.

Part of the reason for the tsunami threat at Makran is the build up of huge piles of submarine sediments. The Arabian oceanic plate is being subducted beneath the Eurasian continental plate, moving northward towards Iran and Pakistan. The sediment that has built up on top of the oceanic plate gets scraped off by the overlying plate and stuck onto the seafloor at the base of the coast.

Over geological time, this process has created one of the largest wedges of sediments on Earth, more than 7km thick in places. Earthquakes can make landslips in the wedge, causing the sediments to tumble down into the deeper ocean. But bizarrely, sometimes they can produce islands, too.

Tuesday’s earthquake shook those offshore sediments to the south of Pakistan. They are mainly muds and sands, rich in the rotted remains of dead sea life that have fallen into the sediments over the millennia. Over time, this material has decomposed to gases like methane. When shaken up on Tuesday, these sediments seem to have erupted in a “mud volcano,” driven by the burping methane from the depths. An island of mud rose above the sea, emitting gas that could be set alight. In fact, locals who tried this had difficulty quenching the flame.

Mud volcanoes have been seen at the Makran subduction zone many times before. The 1945 earthquake triggered a number of mud volcanoes and offshore islands formed in the same region. More recently, one formed off Pakistan in November 2010. They all disappeared soon after, their soft material washed away by the ocean's waves and storms.

It is likely that this week’s new island will only make a temporary appearance, subsiding beneath the waves as the Earth settles back to another period of temporary quiescence. In the meantime, an opportunity remains to really find out more about the nature of these ephemeral islands, before this one passes like a ship in the night.

I'm curious just how quickly the island will erode.Being silt, it won't last long, but would presumably be a rich growing medium - could a fast growing kelp be used to help stabilize the slopes and preserve the island? Could a quick concerted effort preserve the island?

I'm curious just how quickly the island will erode.Being silt, it won't last long, but would presumably be a rich growing medium - could a fast growing kelp be used to help stabilize the slopes and preserve the island? Could a quick concerted effort preserve the island?

I think that it will sink due to subsidence rather than erosional forces.

I'm curious just how quickly the island will erode.Being silt, it won't last long, but would presumably be a rich growing medium - could a fast growing kelp be used to help stabilize the slopes and preserve the island? Could a quick concerted effort preserve the island?

Why yes, this island did appear at the same time hundreds of your kin died. That's why we want to preserve it, since we don't need to look at it every day.

I'm curious just how quickly the island will erode.Being silt, it won't last long, but would presumably be a rich growing medium - could a fast growing kelp be used to help stabilize the slopes and preserve the island? Could a quick concerted effort preserve the island?

I'm curious: what do you think would be the accomplishment balanced against the opportunity to observe the natural process? There's any number of engineering projects that have been undertaken already to "reclaim" land from the sea.

I'm curious just how quickly the island will erode.Being silt, it won't last long, but would presumably be a rich growing medium - could a fast growing kelp be used to help stabilize the slopes and preserve the island? Could a quick concerted effort preserve the island?

Yes, but you'll have a hell of a time building the launch bay, monorail, and other supervillain accoutrements.

Methane is odorless, this is why natural gas is actually mixed with an odorant such as tert-Butylthiol, which gives the rotten eggs smell. If it weren't for this "ungodly smell" (the irony of that statement...) then a lot more people would die from natural gas leaks.

A similar thing happened after the 2004 massive 9.0 Indian Ocean earthquake, the ocean floor rose up 1,189m (3,900 feet) in some places. No island was formed but now the water which was 1,219m (4,000 feet) deep is now only 30m (100 feet) deep, 30m more and it could be an island. http://www.nbcnews.com/id/6791600

I've seen enough Godzilla movies in my day to know what comes next. That's no island. And when it completely wakes from it's slumber, we are going to wish we paid more attention to Pacific Rim's Jaegers...

A similar thing happened after the 2004 massive 9.0 Indian Ocean earthquake, the ocean floor rose up 1,189m (3,900 feet) in some places. No island was formed but now the water which was 1,219m (4,000 feet) deep is now only 30m (100 feet) deep, 30m more and it could be an island. http://www.nbcnews.com/id/6791600

According to what I read yesterday (either AP or BBC) the methane under the ocean floor was the solid Methane Clathrates we've had articles on here about previously. Apparently the heat produced by plates colliding melted the hydrates, which caused them to expand and push the floor up. Very cool stuff.

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